The present invention relates to a hydromechanical transmission mechanism, more particularly for an automobile, in which between a driven shaft and a driving shaft are located a hydrokinetic coupling device of the hydraulic coupler or torque converter type and a reversing device.
More specifically, the invention relates to a transmission mechanism in which the hydrokinetic coupling device and the reversing device are located in a same fluid-filled enclosure, whilst the coupling means between the hydrokinetic device, the reversing device and the driven shaft govern the forward-reverse gear transmission operating conditions.
Among the known devices of this type, there are those in which the reversing device comprises a planetary gear having a central gear wheel, an external toothed rim and planet wheels which mesh with said wheel and said rim.
The central gear wheel is fixed to the driven part of the hydraulic coupling device, the rim is fixed to the driven shaft and the planet wheels are mounted on a planet wheel holder which can either be fixed by means of appropriate coupling means or can rotate with the planet wheels.
Thus, respectively, the reverse gear and forward gear of the transmission are obtained.
One of the disadvantages of these known devices is that such a reversing mechanism does not give the same transmission ratio in reverse gear and forward gear. Moreover, the arrangement of the wheel, planet wheels and rim has very considerable overall radial dimensions, making it necessary to position the reversing mechanism alongside the hydraulic coupling device, therefore increasing the overall axial dimensions of the transmission mechanism.